Japanese Patent Application Publication No. 2005-112300 discloses a one-person vehicle having a body, a steering wheel attached to a front portion of the body, and a driving wheel attached to a rear portion of the body. In addition, Japanese Patent Application Publication No. 2005-82044 discloses a vehicle having a body, and a left wheel and a right wheel which are distant from each other in a widthwise direction of the body and whose positions relative to the body in upward and downward directions are adjustable. In this vehicle, the respective positions of the left and right wheels relative to the body in the upward and downward directions are so controlled as to keep the body horizontal.